CVE-2019-6977 in GD Graphics Library
Summary
by MITRE
gdImageColorMatch in gd_color_match.c in the GD Graphics Library (aka LibGD) 2.2.5, as used in the imagecolormatch function in PHP before 5.6.40, 7.x before 7.1.26, 7.2.x before 7.2.14, and 7.3.x before 7.3.1, has a heap-based buffer overflow. This can be exploited by an attacker who is able to trigger imagecolormatch calls with crafted image data.
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Analysis
by VulDB Data Team • 06/26/2024
The vulnerability CVE-2019-6977 represents a critical heap-based buffer overflow in the GD Graphics Library version 2.2.5, specifically within the gdImageColorMatch function located in gd_color_match.c. This flaw affects PHP versions prior to specific patch releases including 5.6.40, 7.1.26, 7.2.14, and 7.3.1, making it a widespread issue across multiple PHP version lines. The vulnerability manifests when the imagecolormatch function processes crafted image data, creating a scenario where an attacker can manipulate memory allocation and potentially execute arbitrary code through memory corruption.
The technical implementation of this vulnerability stems from inadequate bounds checking within the color matching algorithm of the GD library. When PHP's imagecolormatch function processes images with maliciously constructed color palette data, the gdImageColorMatch function fails to validate the size of input color data against allocated buffer boundaries. This oversight allows attackers to write beyond the allocated memory space, potentially overwriting adjacent memory regions including function pointers, return addresses, or other critical program data. The heap-based nature of the overflow means that the vulnerability occurs in dynamically allocated memory regions, making exploitation more complex but still highly dangerous due to potential memory corruption patterns that can lead to arbitrary code execution.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it provides attackers with potential remote code execution capabilities when the affected PHP applications process untrusted image data. Applications that utilize imagecolormatch for color correction, image processing, or user-uploaded image handling become prime targets for exploitation. This vulnerability aligns with CWE-121, heap-based buffer overflow, and represents a classic example of how graphics processing libraries can become attack vectors when proper input validation is absent. The ATT&CK framework categorizes this under privilege escalation and code execution techniques, as successful exploitation can allow attackers to gain unauthorized system access through carefully crafted image files.
Mitigation strategies for CVE-2019-6977 primarily focus on immediate patching of affected PHP versions to their respective secure releases. System administrators should prioritize updating PHP installations to versions that contain the fixed gd library implementation, ensuring that all affected version lines receive proper security updates. Additionally, implementing input validation measures such as restricting image upload capabilities, sanitizing image data before processing, and employing content security policies can reduce the attack surface. Organizations should also consider implementing web application firewalls and monitoring systems to detect potential exploitation attempts involving image processing functions. The vulnerability underscores the importance of thorough input validation in graphics processing libraries and highlights how seemingly benign image manipulation functions can become critical security risks when proper memory management is lacking.